1. Field of the Invention
The present invention relates to colorants for mass-coloring polyesters, particularly, colorants to be incorporated into polyesters during spinning polyester fibers. This invention also relates to polyester fibers mass-colored with the above colorants and a process for spinning the same, particularly, a mass-coloring and spinning process of polyester fibers.
2. Related Art Statement
Aromatic polyesters represented by polyethylene terephthalate have been extensively used for manufacturing shaped articles, such as fibers, films, plastics, etc., by virtue of their excellent heat and weather resistances. As one of the processes for coloring these aromatic polyesters, there has been a process wherein pigments and/or dyes are mixed and dispersed therein, namely, a mass-coloration process, on which various studies have so far been made.
It has been known that pigments such as carbon black are incorporated into the reaction system. However, only inorganic pigments that are good in heat resistance, such as titanium dioxide, carbon black and the like, have been employable. Alternatively, a so-called color concentrate process is, since pigments are dispersed in the polymer at high temperatures, not only involved in a problem of dispersibility but also comprises complicated steps. Moreover, it has a drawback such that the polymer is degraded at high temperatures in the step of obtaining master chips as well as in the step of mixing them with other chips.
As a so-called "colorant for dope-dyeing" of synthetic fibers, there have been known those having pigments dispersed in a dispersing medium such as ethylene glycol and the like with the aid of a dispersing agent such as an amino alcohol and the like, but they are not satisfactory and also do not resolve problems in practical applications.
Japanese Patent Application Laid-open No. 58-149,311 discloses a colorant comprising a pigment dispersed in an ester of a mono- or polybasic organic acid as an acidic component and a mono- or polyhydric alcohol as an alcoholic component. Further, Japanese Patent Application Laid-open No. 60-45,689 discloses a liquid colorant for mass-coloring polyester fibers, comprising a liquid polyester and a pigment admixed therewith, and Japanese Patent Application Laid-open No. 60-45,690 discloses a colorant wherein a pigment is incorporated into a liquid polyester having an acid value of about 1.0 and a viscosity of about 10 poises, obtained from adipic acid, ethylene glycol and 2-ethylhexyl alcohol, as starting materials. In the case where the colorants are mixed and dispersed in polyesters, particularly, the aromatic polyesters represented by polyethylene terephthalate, the heat stability of the polyesters is lowered so that problems, such as difficulties in manufacture as well as discoloration caused by heat during melt-spinning, still remain unsolved. Also in the case where there are employed the colorants comprising, as a dispersing medium, a liquid aliphatic polyester obtained by reacting adipic acid with ethylene glycol, etc., the liquid aliphatic polyester lowers the inherent viscosity of the polyester to be colored so that not only, for example, filament breakages occur more frequently, causing impairment of the spinnability, but also filament qualities such as tenacity, elongation or the like are deteriorated. Further, the liquid polyester wherein 2-ethylhexyl alcohol is used as a part of the starting materials is not satisfactory in respect of heat resistance and, therefore, presents problems such that generation of decomposed gases, discoloration, deterioration of physical properties, etc. are brought about on the mass-colored polyesters, during spinning of the polyesters.